Hearthpwn

This is a competitive mill deck.  The goal is to kill your opponent through fatigue, though the low-cost big cards can bring enormous early pressure.  The deck is capable of delivering some nice win streaks and is a ton of fun to play.  Opponents generally have no idea what you are doing until it's too late.

General Strategies

Coldlight Oracle is the king of this deck.  Never play him when you cannot immediately call him back into your hand through Youthful Brewmaster, Shadowstep, or Vanish unless you have his twin in your hand as well.

The other key card is Lorewalker Cho, of course.  You are almost certain to lose if you do not draw either the Oracle or Cho after a few rounds.  That is the reality of any deck that heavily relies on one or two critical cards.

Ideally you will open with Cho on round 2, King Mukla on round 3, and Anub'ar Ambusher on round 4.  Starting a game with two 5-5's and Cho-insanity causes all sorts of difficulties for the other player.  More commonly you will coin into any of the large 3-drops, including Dancing Swords and Deathlord.

Assuming you have drawn an Oracle off the bat, milling typically begins in the middle rounds while your opponent is trying to figure out how to solve your large minions.  Focus on killing as many of his minions as possible; only go for face when the board is clear.  Vanish is your big board clear, and it kills any minions that cannot fit into a 10-card hand.  This can be brutal when you have been successfully milling and your opponent has a full board.  Similarly, Sap is your spot removal for big threats.  It works as a 2-mana Assassinate against a full hand.

By far the most entertaining games involve playing Faceless Manipulator to double Cho.  However, that happens so infrequently that the Manipulator is usually better suited to copy a big taunt to buy yourself time to mill.  I have gone back and forth about replacing the Manipulator with a second Sludge Belcher, but I so often found myself holding two Belchers that I stuck with the Manipulator.

Match-Ups

It should go without saying that this deck works far better against control and tempo decks than aggro.  I have won over 100 games with this deck, but I have yet to beat Shockadin once.  Zoo-type decks are difficult but not impossible, and the general meta move away from Zoo over the past few months has made the deck more viable.

Handlock decks are the dream match-up.  Against any 'Lock, you want to hold off on milling until you know you can burn his deck; the more he soul siphons before he realizes what you're doing, the better.

T'his deck is generally effective against Priests.  My win rate against them is well over 50%, if not closer to 75%.  Their present popularity has boosted the viability of the deck.

It is important to keep your eye out for ways to use the opponent's draw cards against them.  A great example is taking advantage of any fool who unwittingly plays an Acolyte of Pain - grab your dagger and stick him for one damage.  This is equally true against Priests.  Whenever they play the ubiquitous Northshire Cleric, injure but don't kill her.  The player will think you are a total beginner and heal her back up.

Mage secret decks seem to be back in style now, and Cho produces a copy of any secret they play.  This not only gives you a copy of the card, but it lets you know what the secret is.  Another seldom-employed mechanic involves the Ice Block secret.  If you have the Mage in fatigue and you trigger Ice Block on your turn, the Mage will draw a card to begin her turn and die immediately.  That can make for some fun wins.

And on those fine occasions when a Shaman drops an early Mana Tide Totem (or the rare Nat Pagle), enjoy a laugh, watch his cards embarrassingly burn off, and notch the victory.

Mulligan Notes

Always keep the Oracle, Cho, and Mukla.  If you do not get an Oracle in your first draw, mulligan all other cards.  If you are lucky enough to draw an Oracle, keep the most sensible combination of Shadowstep, Backstab, SI:7 Agent, Dancing Swords, Deathlord, and Anub'ar Ambusher that you have.  Always mulligan away Preparation and cards costing five or more mana.

Card Considerations

I was running one or two Mana Wraiths for a long time, but they almost always died the next turn and therefore rarely had a substantial impact on the game.  I recently replaced them with a second Preparation and a single Nerub'ar Weblord, and the Weblord draws so much attention from the opponent that I am considering doubling him in place of the Preparation I put back in.  Of course, the Weblord jacks up the cost of the Oracle, but any card that draws the opponent's attention away from your face and slows them down is a winner here.

And while Kidnapper seems like an obvious fit for this deck, it costs way too much to use with any effectiveness.  The 5-3 body it leaves behind is easily dealt with by the late stage of the game when he can be played.  Moreover, the six total bounce cards used to get the Oracle back in your hand are more than sufficient.

The two Deathlords are fundamental to this deck despite their somewhat-frightening deathrattles.  In addition to a cheap 8-health taunt, he pulls extra cards out of the deck without triggering those cards' battlecries and is especially obnoxious where his death is followed by a Sap or Vanish.  Naturally, combining him or Dancing Swords with Baron Rivendare works as the most effective milling combinations the deck offers.

Finally, there is absolutely no card draw other than the Oracles.  I have experimented with Shiv, Fan of Knives, Bloodmage Thalnos, etc., but they invariably wind up causing you to mill yourself.  That's no way to die.  You're either going to draw your Oracle and mill the unsuspecting victim or lose to someone who will think you have no clue what you're doing.

Have fun.

--- Revision 1 ---

I removed Nerub'ar Weblord in favor of Doomsayer.  Like Mana Wraith, the Weblord had a nasty habit of clogging your own plans and died too easily.

So far the Doomsayer has been a wonderful addition, and he operates differently than you would expect in this deck.  In addition to his board wipe ability, he potentially (1) absorbs 7 damage that would have gone to your face when the opponent takes him out, (2) absorbs a silence that would have hit the Belcher, Swords, or Deathlord, or, amusingly, (3) shuts down the opponent when played immediately after a Vanish.